Method of making seamless tubes



Patented Jan. g, WEQ:

wen STATES PATENT 'FIE I 1,942,541 us'rnop or MAKING snammss TUBENo'Di-awing. Application April 19,1930

- Serial No. 445,819

3 Claims. (ci'so-ez) This invention relates to the manufacture ofseamless tubes and more particularly to a method of producing largediameter, thin-walled tubes of commercial lengths.

'6 Heretofore it has been the general commercial practice inmanufacturing seamless tubes to heat a solid blank up to the desiredtemperature, then pierce the blank to form a tube having a diametersomewhat larger than the finished tube and a wall thickness of about onehundred and forty per cent. greater than the wall of the finished tube.This roughly formed tubing is then rolled in the plug rolling mill toreduce the wall thickness and to reduce the diameter to somewhat-less llthan the finished diameter required.

The reduced tube is'then passed directly an without reheating throughcross-rolling machines for the purpose of smoothing the surface andequalizing the wall thickness without any material change in the wallthickness. However, during this last operation, the diameter of the tubeis slightly enlarged beyond the diameter of the finished tube. The tuberesulting from this last operation is then passed through sizing rollsto reduce it to flnalfinished diameter.

The well known and commercial method described above is practical andsuccessful on tubes up to approximately four inches in diameter, havingthe commercial range of wall thickness. I In such method, involving onlya single piercing operation, the pierced billet is generally takendirectly to the plug rolling mill. The temperature changes in thepiercing operation are comparatively slight and not suflicient to affectthe plug rolling operation;

For tubes beyond about four inches in diameter, a single piercingprocess involves a very large amount of work and a rapid deformation ofthe metal, which tend to injure the material or .to destroy itsappearance even when its strength is not injured. 0n the other hand, theuse of a double or other multiple piercing operation, while free fromthe bad features of the single operation, will introduce a variation intemperature, causing difliculties in the subsequent rolling operations,namely-a tendency to tear the metal and a decrease in the yield ofsalable product.

We have discovered that by a comparatively short reheating operation thedoubly pierced product can be rolled without producing these defects.The reheating serves to'ofl-set two incidents to the double piercing.Thedouble piercing operation increases the time: interval be-,

tween the moment when the metal leaves the 5 initial heating furnace andthe moment when called thin-walled tubes. N'ot only is there a it entersthe rolling mill, and thus involves a considerable cooling of the work.But'the original temperature cannot be varied except within a narrowrange, not sufficient for our purpose because to do so interferes withthe success of the piercing operation. The difiiculty, due to cooling bydouble piercing, is particularly apparent when the ratio of wallthickness to outside diameter in the finished tube is within less thanabout three per cent; that is, what may be material lowering of thetemperature of the tube as a whole but there is also a considerablevariation in its temperature from end to end, due to the nature of thesecond piercing operation, bringing the wall thickness to about one halfor one-third of that produced in the first piercing operation.

We have found, however, that with an initial temperature suitable forpiercing and with. a short reheating after piercing, the difiicultiesreferred to can be obviated and tubes of large size and great length andcomparatively thin walls can be produced with an increased percentage ofsalable yield and an improved quality of the product.

The tube after the last piercing operation needs to be left in areheating furnace only a few minutes, one or two minutes generally, inorder to make it suitable for successful rolling and also to unify thetemperature from end to end 'within practical limits.

The most important effect of this reheating, is the capability ofproducing the tubes in comparatively great lengths by rolling them at atemperature which is approximately uniform from end to end. Thisunifying of. the temperature is due largely to the mere holding of thetube between the last piercing and the first rolling operation, sincethere is always a tendency for the heat to distribute itself fairlyrapidly throughout the length of the highly conductive steel; and thevalue of the reheating operation is largely in preventing loss of heatduring such unifying period while the total heat of the tube is beingaveraged throughout. its length.

In view of our discoveries we therefore have developed a practical andsuccessful method of producing commercial, thin-walled seamless tubeshaving agreater diameter than about four inches which consists inheating a round solid blank or billet to the proper piercingtemperature, piercing the heated billet to form a rough tube having awall thickness of from approximately 340 to 440 per cent. greater thanthe no wall thickness of the finished tube, then again piercing the oncepierced tube without reheating to increase its diameter and reduce itswall thickness to approximately 140 per cent. greater than 5 the wallthickness of the finished tube.

Due to this double piercing step, the tube blank is too, cool and itstemperature too uneven to permit successful plug rolling; therefore, wenext pass the tube into a temperature equalizing furnace where the tubeis brought to an equal temperature throughout its length suitable forthe further finishing operation. The tube is generally retained in thereheating furnace from one 'to two minutes.

After the temperature of the tube has been equalized and brought to theproper plug rolling temperature it is plug rolled, cross-rolled andsized in the usual manner without further heating and results in theproduction of a large diameter (a diameter of more than four inches)thinwalled tube of commercial length, a thin-walled tube being that inwhich the ratio of wall thickness to outside diameter approximates oneand eter less than about three per cent. which'consists in heating around solid blank or billet to the proper piercingptemperature, piercingsaid heated billet to form a rough tube having a wall thickness of fromapproximately 340 to 440 per cent. greater than the wall thickness ofthe finished tube, then again piercing said once pierced tube withoutreheating to increase its diameter and reduce its wall thickness toapproximately 140 per cent. greater than the wall thickness of thefinished tube, then carrying the twice pierced tube in a furnace forabrief period, of the order of one or two minutes, immediately after thelast piercing operation to produce a uniform temper- 'ature from end toendof said pierced tube, then removing said uniformly heated tube andplug rolling, cross rolling and sizing said tube to finished size.

2. The method of making-thin walled seamless tubes of greater than fiveand one-half inches in diameter and of standard commercial lengths andhaving a ratio-of wall thickness to outside diameter less than aboutthree per cent. which consists in heating a round solid blank or billetto the proper piercing temperature, piercing said heated billet to forma rough tube having a wall thickness of several times the wall thicknessof the finished tube, then again piercing said once furnace for-a briefperiod, of the order of one or two minutes, immediately after the lastpiercing operation to produce a uniform temperature from end to end ofsaid pierced tube, then removing said uniformly heated tube and plugrolling, cross rolling and sizing said tube to finished size.

3. The method of making'thin-walled seamless tubes of greater than fiveand one-half inches in diameter and of standard commercial lengths andhaving a ratio of wall thickness to outside diameter lessthan about 3per cent. which consists in heating a round solid blank or billet to theproper piercing temperature, piercing said heated billet to increase itslength and diameter and form a rough tube having a wall thickness ofseveral times the wall thickness of the finished tube and less than 450per cent. greater than the wall thickness of the finished tube, thenagain piercing said once pierced tube without reheating to increase itslength and diameter and reduce its wall'thickness to less than 150 percent. greater than the thickness of the finished tube, then carrying thetwice pierced tube in a furnace for a brief period, of the order of oneor two min- J utes, immediately after the last piercing operation toproduce a uniform temperature from end to end of said pierced tube, thenremoving said uniformly heated tube and plug rolling, cross-rolling andsizing said tube to finished size.

JERRY J. DUNN. PETER c. PATTERSON.

